Extended Data Table 2. Complete or partial sweeps of Eastern Hemisphere-origin AIV internal genes across Western Hemisphere AIV in recent decades.

	Total No. of Western Hemisphere AIV full-length sequences, 2009-2013	No. in West-1 clade*	No. in West-2 clade	No. in West-3 clade
PB1	1059	0 (0 %)*	1059 (100%)†	0 (0%)‡
PA	1052	1 (0.1%)*	420 (39.9%)§	631 (60.0%)∥
NP	886	12 (1.4%)*	863 (97.4%)¶	N/A
NS1/2	560☆	6 (1.1%)*	554 (98.9%)#	N/A

^*This is the pre-20^th century Western Hemisphere AIV lineage (see Fig. 2 for clade designations).

^†Migrated from Eastern Hemisphere after ~1945 and before ~1955.

^‡Migrated from Eastern Hemisphere after ~1945 and before ~1960.

^§Migrated from Eastern Hemisphere after ~1921 and before ~1940.

^∥Migrated from Eastern Hemisphere after ~1965 and before ~1969.

^¶Migrated from Eastern Hemisphere after ~1940 and before ~1945.

^#Migrated from Eastern Hemisphere after ~1928 and before ~1940.

^**NS A lineage sequences only; there were an additional 262 NS B lineage sequences (30% of 822 total NS sequences).